CYCLIC STRENGTH AND BOND PERFORMANCE OF A DUCTILE HYBRID FRP BAR FOR CONCRETE STRUCTURES

摘要

In regions of moderate to high seismicity, reinforced concrete (R/C) structures are designed based on their ability to absorb seismic energy. This absorption capacity exists due to the ability of the reinforcement to yield, thereby producing large inelastic strains. The low-cycle fatigue behavior of a Ductile-Hybrid FRP (DHFRP) bar was investigated at Drexel University by placing the bars in beam-column concrete elements. Unlike most current FRP bars, the DHFRP bar has a behavior that simulates the stress-strain characteristics of conventional steel reinforcement (1, 2). The DHFRP bar exhibits a tri-linear stress-strain behavior, which shows significant material toughness for all bar sizes. These bars are produced using a combination of both traditional pultrusion and braiding processes simultaneously, creating a 'Braidtrusion' process, and have been produced in a 10-mm diameter prototype size. The bars are a material hybrid of aramid (Kevlar 49) fibers and carbon (Thornel P-55S). The design methodology and manufacturing process is described in (3) and (4). The energy absorption capacity of the material was demonstrated through the hysteretic load-deflection and moment-rotation behavior of the beam-columns, and through definitions of ductility indices based on displacement, rotation, and curvature. Bond pullout tests were also conducted to determine the amount of slip and bond stress required to obtain the bar development length. A unique bond failure mode, based on the failure mode of DHFRP was observed. Bond strengths were large due to the rough surface texture and integrated rib system of the DHFRP bars.